Vehicles may be fitted with evaporative emission control systems such as onboard fuel vapor recovery systems. Such systems capture and reduce release of vaporized hydrocarbons to the atmosphere, for example fuel vapors released from a vehicle gasoline tank during refueling. Specifically, the vaporized hydrocarbons (HCs) are stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel. The fuel vapor recovery system may include one more check valves, ejectors, and/or controller actuatable valves for facilitating purge of stored vapors under boosted or non-boosted engine operation.
Various approaches have been developed for detecting undesired evaporative emissions and/or degraded components in such fuel vapor recovery systems. However, the inventors have recognized several potential issues with such methods. The inventors have recognized that, in particular, it may be difficult to diagnose one or more valves controlling flow of purge gases from the fuel vapor canister to the intake passage upstream of the compressor. For example, it may be difficult to determine if a check valve positioned downstream of a canister purge valve and upstream of an ejector and intake passage, is stuck in an open position. If such a check valve is stuck in an open position, during natural aspiration (e.g., non-boosted) operation, intake air through the open path may be sucked into the engine. This unmetered air may cause the air-fuel ratio to decrease (and become leaner than desired), thereby increasing NOx emissions. Specifically, the inventors have recognized that it may be difficult to diagnose a position of such a check valve during regular boosted or non-boosted (e.g., vacuum) modes without the aid of additional sensors. However, adding sensors for this diagnosis may increase engine costs and complicate engine control.
The inventors herein have recognized these issues, and have developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising storing fuel vapors from a fuel system, which supplies fuel to an engine, in a fuel vapor storage canister, coupling the canister to an air intake of the engine through a second path having a second check valve which prevents unmetered air from being drawn into an intake manifold of the engine, and diagnosing whether the second check valve is stuck open based on a temperature change of the canister.
As one example, the method may include controlling pressure in the second path via a pump positioned in a vent line between the fuel vapor canister and atmosphere, where diagnosing whether the second check valve is stuck open includes reducing pressure in the second path via the pump. In some examples, reducing pressure in the second path via the pump draws atmospheric air across the second check valve under conditions where the second check valve is stuck open. Furthermore, the method may include controlling a flow of fuel vapors from the fuel system to the fuel vapor storage canister via a fuel tank isolation valve, where the fuel tank isolation valve is in a closed configuration during reducing pressure in the second path via the pump to prevent fuel vapors from being drawn into the fuel vapor storage canister.
In such an example, the method may include indicating the second check valve is stuck open responsive to the temperature change at the fuel vapor canister decreasing to a canister temperature change threshold. The method may further include preventing positive pressure with respect to atmospheric pressure from being communicated to the fuel vapor canister under conditions of positive pressure in the intake manifold via a first check valve in a first path, where diagnosing whether the second check valve is stuck open includes an indication that the first check valve is not stuck open. The method may further include diagnosing whether the second check valve is stuck open responsive to an indication that the first path and the second path are free from undesired evaporative emissions. The method may further include diagnosing whether the second check valve is stuck open while the engine is not in operation.
In this way, the second check valve may be periodically diagnosed as to whether the second check valve is stuck open, where responsive to an indication that the second check valve is stuck open, mitigating actions may be taken to prevent undesired emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.